A technique called a Multimedia Broadcast and Multicast Service (hereinafter, MBMS) has recently been standardized for distributing multimedia contents such as motion pictures and music, under the Wideband-Code Division Multiple Access (W-CDMA) system.
The MBMS has enabled broadcasting service of the contents utilizing the Forward Access Channel (hereinafter, FACH), which has conventionally been serving as the common channel, to thereby save the radio resource in response to the increase in demand for the multimedia service.
The FACH refers to the downlink common channel transmitted by the base transceiver station, which is utilized for transmitting control information and user data.
An example of a system related to the MBMS is a system configured with the base transceiver station and a base transceiver station controller. In such a system, when a plurality of cells exists under control of the base transceiver station, the base transceiver station allocates each of the cells with the FACH for distributing the contents and transmits the same contents to the respective FACH.
Multimedia service provided by the MBMS (hereinafter, MBMS service) is different from multimedia service using an existing common channel in that high data rate is required.
For example, in the MBMS service, data rate service of about 128 kpbs or 256 kpbs has to be provided in the entire area covered by each cell using the common channel.
Consequently, to provide high-data-rate service as the MBMS service so as to cover the entire cells, the base transceiver station needs a very large amount of transmit power.
There is a possibility that, by providing the MBMS service, the base transceiver station consumes power which can be used in other speech calls and packet access calls.
A technique for controlling the transmit power for a multicast signal in a base station is described in Patent Document 1.    [Patent document 1] Japanese Laid-open patent publication NO. 2001-292096